Add Service Bindings support

CloudFlare Workers Service Bindings:
https://developers.cloudflare.com/workers/platform/bindings/about-service-bindings/

Inspiration:
#183

worker/src/env.rs

@@ -1,6 +1,5 @@
 use crate::error::Error;
-use crate::Result;
-use crate::{durable::ObjectNamespace, DynamicDispatcher};
+use crate::{durable::ObjectNamespace, DynamicDispatcher, Fetcher, Result};
 
 use js_sys::Object;
 use wasm_bindgen::{prelude::*, JsCast, JsValue};
@@ -51,6 +50,12 @@ impl Env {
     pub fn dynamic_dispatcher(&self, binding: &str) -> Result<DynamicDispatcher> {
         self.get_binding(binding)
     }
+
+    /// Get a [Service Binding](https://developers.cloudflare.com/workers/runtime-apis/service-bindings/)
+    /// for Worker-to-Worker communication.
+    pub fn service(&self, binding: &str) -> Result<Fetcher> {
+        self.get_binding(binding)
+    }
 }
 
 pub trait EnvBinding: Sized + JsCast {

worker/src/fetcher.rs

@@ -1,8 +1,8 @@
-use wasm_bindgen::JsCast;
+use wasm_bindgen::{JsCast, JsValue};
 use wasm_bindgen_futures::JsFuture;
 use worker_sys::{Fetcher as FetcherSys, Response as ResponseSys};
 
-use crate::{Request, RequestInit, Response, Result};
+use crate::{Request, RequestInit, Response, Result, env::EnvBinding};
 
 /// A struct for invoking fetch events to other Workers.
 pub struct Fetcher(FetcherSys);
@@ -32,6 +32,36 @@ impl Fetcher {
     }
 }
 
+impl EnvBinding for Fetcher {
+    const TYPE_NAME: &'static str = "Fetcher";
+}
+
+impl JsCast for Fetcher {
+    fn instanceof(val: &wasm_bindgen::JsValue) -> bool {
+        val.is_instance_of::<Fetcher>()
+    }
+
+    fn unchecked_from_js(val: wasm_bindgen::JsValue) -> Self {
+        Self(val.into())
+    }
+
+    fn unchecked_from_js_ref(val: &wasm_bindgen::JsValue) -> &Self {
+        unsafe { &*(val as *const JsValue as *const Self) }
+    }
+}
+
+impl From<Fetcher> for JsValue {
+    fn from(service: Fetcher) -> Self {
+        JsValue::from(service.0)
+    }
+}
+
+impl AsRef<wasm_bindgen::JsValue> for Fetcher {
+    fn as_ref(&self) -> &wasm_bindgen::JsValue {
+        &self.0
+    }
+}
+
 impl From<FetcherSys> for Fetcher {
     fn from(inner: FetcherSys) -> Self {
         Self(inner)

worker/src/router.rs

@@ -10,7 +10,7 @@ use crate::{
     http::Method,
     request::Request,
     response::Response,
-    Result,
+    Result, Fetcher,
 };
 
 type HandlerFn<D> = fn(Request, RouteContext<D>) -> Result<Response>;
@@ -94,6 +94,12 @@ impl<D> RouteContext<D> {
     pub fn param(&self, key: &str) -> Option<&String> {
         self.params.get(key)
     }
+
+    /// Get a [Service Binding](https://developers.cloudflare.com/workers/runtime-apis/service-bindings/)
+    /// for Worker-to-Worker communication.
+    pub fn service(&self, binding: &str) -> Result<Fetcher> {
+        self.env.service(binding)
+    }
 }
 
 impl<'a> Router<'a, ()> {